1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump slip joint internal seal used to provide an effective means of sealing the joint between an inlet mixer and a diffuser of a BWR jet pump assembly.
2. Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and may be supported by conventional jet pump restrainer brackets. While conventional jet pump restrainer brackets may provide system stiffness that mitigates vibration of system components, slip joint flow induced vibration (FIV) and leakage may still occur between the inlet mixers and the diffusers. In particular, slip joint FIV is the root cause of the major damage to many of the jet pump components in a BWR. Furthermore, insertion and stabilization of the inlet mixers within the diffusers may cause the inlet mixers to remain slightly off-center within the diffuser, causing further slip joint FIV and leakage.
Conventionally, many attempts have been made to reduce slip joint FIV. For instance, slip joint clamps, auxiliary wedges at the set screws of restrainer brackets, labyrinth seals, restrainer bracket pad repair, and replacement main wedges have all been used. These efforts generally involve either clamping the inlet mixer to the diffuser, or constraining the inlet mixer to the riser pipe via the restrainer bracket. While these conventional solutions have provided some additional system stiffness, none of the solutions address actual leakage between the inlet mixers and diffusers. Therefore, none of the conventional solutions prevent the main vibration forcing function involved in slip joint FIV from occurring.